Funnel hole for intramedullary nail

ABSTRACT

An intramedullary nail may include a shank with a centerline defined along a length thereof. The intramedullary nail may also include a channel with a channel axis transverse to the centerline. The channel may have an obround shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane containing the channel axis. A proximal edge of the channel within the second cross-sectional plane may form a first angle relative to the channel axis and a distal edge of the channel within the second cross-sectional plane may form a second angle relative to the channel axis that is different from the first angle.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of the filing date of U.S.Provisional Patent Application No. 63/031,701 filed May 29, 2020, thedisclosure of which is hereby incorporated herein by reference.

BACKGROUND

Intramedullary nails are known solutions for treating injuries to bone,such as fractures or breaks. For example, it is known to use anintramedullary nail to treat a fracture in a body of a femur, or to usean intramedullary nail in cooperation with a lag screw to treat afracture in a femoral neck. Such intramedullary nails may have elongateshapes, including a relatively thin and cannulated shank extending froma head of the nail that is intended to fit through a medullary cavity ofthe bone being treated. The cannulation along the entire length of thenail is used for a surgeon to insert k-wires for guiding the nail duringinsertion into the intramedullary canal of the long bone such as a femuror tibia.

In some applications, one or more locking screws are inserted throughthe bone and through corresponding channels located near a distal end ofthe shank. Because the shank may deflect while being driven into thebone by an amount that is difficult to predict with certainty, workablelocations and angles for accurate placement of the locking screws islikely to vary between patients. Additional steps may be required beforeinserting the locking screws, such as scanning or imaging the bone andnail after the nail is implanted to determine the final location of thechannels.

BRIEF SUMMARY

An intramedullary nail may be designed such that locking screws may beinserted through channels at a distal end of the nail after the nail isinserted into a long bone while taking into account any flexure of thenail that occurs during insertion. The flexion of the nail occurs due tothe fact that the intramedullary canal of a long bone is curved andtherefore the inserted nail follows the anatomy of the bone. Such a nailmay be designed such that a drill may be inserted through the bone at agiven location and angle relative to the bone, or relative to a head ofthe nail, without contacting a proximal or distal edge of thecorresponding channels.

To that end, part of the channels may have a funnel shape. The channelsmay generally be of constant cross-section, such as being cylindrical inshape, and extend in a direction perpendicular to the centerline of thenail, except for the funnel shaped portions. The funnel shape may taperfrom being wider at one side of the nail to narrower at the other side.The taper may be along only a part of a depth of the channel, and thechannel may include an inflection point separating a tapered portionfrom a portion of constant size. The channels may be of a constant widthrelative to a lateral direction of a shank of the nail, but may taperfrom longer to shorter relative to a lengthwise direction of the shankof the nail. Such channels may therefore have an obround shape at leastat a wider end thereof, and through at least part of a depth thereof.

In another aspect, an intramedullary nail may include a shank with acenterline defined along a length thereof. The intramedullary nail mayalso include a channel with a channel axis transverse to the centerline.The channel may have an obround shape in a first cross-sectional planeperpendicular to the channel axis at the centerline and a taperedprofile in a second cross-sectional plane containing the channel axis. Aproximal edge of the channel within the second cross-sectional plane mayform a first angle relative to the channel axis and a distal edge of thechannel within the second cross-sectional plane may form a second anglerelative to the channel axis that is different from the first angle.

In some arrangements, opposed proximal and distal ends of the channelmay each be defined by a round end extending along respectivenon-parallel axes. Opposed sides of the channel may be planar and extendbetween the two round ends to define the obround shape.

In some arrangements, the channel is fully internally threaded.

In some arrangements, the channel defines a circular opening at asurface of the shank.

In some arrangements, the two non-parallel axes may each intersect thecenterline.

In some arrangements, the first angle may be non-zero and the secondangle may be zero.

In some arrangements, the nail may include an obround opening in theshank that feeds into the channel, and at least part of a perimeter ofthe obround opening may be chamfered.

In some arrangements, an angle between the two non-parallel axes may bebetween 3° and 7°.

In some arrangements, the angle between the two non-parallel axes may be6.5°.

In another aspect, the shank may be capable of elastic deformationacross a range of deflection of a distal tip of the shank on the secondcross-sectional plane. A ratio of the range of deflection of the distaltip of the shank to a total length of the nail may be at least 1:30. Arectangular area may exist on the second cross-sectional plane that mayextend through the channel without crossing a proximal or distal edge ofthe channel at any position within the range of tip travel.

In some arrangements, the ratio of the range of deflection of the distaltip of the shank to the total length of the nail may be 1:24.

In some arrangements, the shank may define a bore extending along thecenterline and dividing the channel into two aligned apertures.

In another aspect, a method for treating injury to a femur may includeinserting an intramedullary nail into the femur generally along theanatomical axis of the femur. The nail may include a shank with acenterline defined along a length thereof. The shank may have a channelwith a channel axis transverse to the centerline. The channel may havean obround shape in a first cross-sectional plane perpendicular to thechannel axis at the centerline and a tapered profile on a secondcross-sectional plane containing the channel axis at the centerline. Themethod may also include inserting a screw through a predeterminedlocation of the femur.

In some arrangements, the nail may include an obround opening in theshank that feeds into the channel. The nail may be implanted in thefemur with the obround opening oriented in an anterior directionrelative to the femur.

In some arrangements, the nail may be implanted in the femur such thatthe tapered profile narrows toward a posterior direction relative to thefemur.

In some arrangements, the method may further include drilling throughthe femur and the channel at a predetermined location of the femur fromthe anterior direction toward the posterior direction.

In some arrangements, the screw may engage at least a portion of thechannel to accommodate flexion of the intramedullary nail that occursduring implantation.

In some arrangements, a method of designing an intramedullary nail mayinclude estimating an anticipated range of flexion of a shank of anintramedullary nail on a flexion plane corresponding to flexion of thenail during a procedure for implanting the nail in a bone. The methodmay include defining a fixed position for a cylindrical fixation elementrelative to a head of the nail located at a proximal end of the nail.The fixed position may be such that the cylindrical fixation elementwould extend transverse to and intersect the shank at any position ofthe shank within the anticipated range of flexion. The method may alsoinclude selecting respective locations and angles for a proximalextremity of a channel disposed through a distal half of the shank and adistal extremity of the channel such that the cylindrical fixationelement located at the fixed position would extend through the channelwithout crossing the proximal extremity or the distal extremity of thechannel at any degree of flexion of the shank within the anticipatedrange of flexion.

In some arrangements, the method may include defining an additionalfixed position for an additional cylindrical fixation element. Themethod may include selecting respective locations and angles forproximal and distal extremities of an additional channel disposedthrough the distal half of the shank such that the additionalcylindrical fixation element located at the additional fixed positionwould extend through the additional channel without crossing theproximal or distal extremity of the additional channel at any degree offlexion of the shank within the anticipated range of flexion.

In some arrangements, a method for treating injury to a femur using theintramedullary nail may include inserting the nail into the femurgenerally along the anatomical axis of the femur while allowing flexionof the nail within the femur. The method may also include, after thenail is inserted into the femur, inserting a screw through the femur andchannel at a location and angle relative to the head of the nailcorresponding to the fixed position of the cylindrical fixation element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional elevation view of a nail according to afirst arrangement.

FIG. 1B is an elevation view of a nail according to a secondarrangement.

FIG. 2A is a side elevation view of a tip portion of the nail of FIG.1A.

FIG. 2B is a cross-sectional view along line 2B-2B of FIG. 2A.

FIG. 2C is another side elevation view of the tip portion of the snailshown in FIG. 2A

FIG. 3 is a cross-sectional elevation view of the nail of FIG. 1A inthree degrees of deflection.

FIG. 4 is a cross-sectional elevation view of a portion of a nailaccording to a third arrangement.

FIG. 5 is a perspective view of a targeting device for use with thenails of FIG. 1A, 1B, or 4.

FIG. 6 is a cross-sectional elevation view of the targeting device ofFIG. 5 guiding a drill into the nail of FIG. 1A, 1B, or 4 throughvarious stages of deflection.

DETAILED DESCRIPTION

An intramedullary nail 10 illustrated in FIG. 1A includes a head 14, acone 16 tapering to a narrower diameter from the head 14, and a shank 18extending from the cone 16. The nail 10 extends along a centerline X.The centerline X is illustrated as straight in FIG. 1A, but the shank 18is flexible with respect to the head 14, meaning the centerline X mayhave a curved profile depending on the shank's 18 state of flexure. Theshank 18 may have a non-linear resting position, which may, for example,include the centerline X curving toward a posterior direction P withincreasing distance from the head 14 such as in the alternativearrangement shown in FIG. 1B. The shank 18 may therefore be able tocurve further toward the posterior direction P than an opposite anteriordirection A.

A distal portion 20 of the shank terminates in a point 22. The distalportion 20 illustrated herein is a distalmost half of the shank 18. Thedistal portion 20 includes at least one channel 28 extendingtherethrough. In the illustrated arrangement, the distal portion 20includes a first channel 28 a and a second channel 28 b extendinganterior to posterior through the nail 10. The second channel 28 b iscloser to the point 22 and has a greater width along the centerline Xthan the first channel 28 a.

As shown in more detail in FIG. 2A, the first and second channels 28 a,28 b have first and second chamfered anterior openings 34 a, 34 b,respectively. Both anterior openings 34 a, 34 b have obround shapes fromthe perspective of FIG. 2A extending lengthwise parallel to thecenterline X. Here, “obround” refers to any of a stadium shape, anorthographic projection of a capsule, a shape including two opposedsemicircular, or approximately semicircular, edges joined by twoparallel lines, or shapes generally similar to the foregoing. However,“obround shape” is used in an approximate sense to accounts for the factthat the curved perimeter of the shank 18 gives the anterior openings 34a, 34 b non-planar profiles.

Turning to FIGS. 2B and 2C, the first and second channels 28 a, 28 bfurther include first and second posterior openings 38 a, 38 b,respectively. The first posterior opening 38 a is circular, having adiameter equal to a lateral width of the first anterior opening 28 a,while the second posterior opening 38 b is obround, having an equallateral width to that of the second anterior opening 28 b, but a lesserwidth parallel to the centerline X.

The first channel 28 a defines a centered orthogonal axis 46 extendingperpendicular to the centerline X and through a centerpoint of the firstposterior opening 38 b. A first distal edge 50 a of the first channel 28a extends parallel to the centered orthogonal axis 46. A distal part ofthe first channel 28 a defines a cylinder centered on the centeredorthogonal axis 46. The funnel shape of the first channel 28 a isfurther defined by a first skew axis 47 angled with respect to thecentered orthogonal axis 46. Here, “angled” is used to mean that thefirst skew axis 47 extends at a non-zero angle relative to the centeredorthogonal axis 46. The first skew axis 47 extends parallel to a firstramped portion 51 a of a proximal edge 54 a of the first channel 28 a.In a preferred arrangements, the first skew axis 47 extends at an angleof 6.5° relative to the centered orthogonal axis 46. In otherarrangements, this angle can be in the range of 3.5° to 9.5°, or 4° to8°, or 6° to 7°. The first ramped portion 51 a extends distally andposteriorly away from the first anterior opening 34 a to a firstinflection point 52 a at which the first channel 28 a reaches a circularcross sectional shape. The volume below this first inflection point 52 ato first posterior opening 38 a is a cylindrical zone of first channel28 a, as indicated above. The volume above first inflection point 52 ato first anterior opening 34 a at the distal side of first channel 28 abetween centered orthogonal axis 46 and first distal edge 50 a is alsopart of a cylindrical volume, i.e. a half cylinder, of first channel 28a. The volume above first inflection point 52 a to first anterioropening 34 a at the proximal side of first channel 28 a between centeredorthogonal axis 46 and first ramped portion 51 a is a conical zone offirst channel 28 a. Together, these 3 volumes make up the entire volumeof first channel 28 a.

The first ramped portion 51 a also extends along a most proximalextremity of a half cylinder defined by the first channel 28 a thatextends along the first skew axis 47 between the first inflection point52 a and the first anterior opening 34 a. The first proximal edge 54 ais defined by the first ramped portion 51 a, the first inflection point52 a, and a first orthogonal portion 53 a, collectively. The firstorthogonal portion 53 a of the first proximal edge 54 a extends parallelto the centered orthogonal axis 46 between the first inflection point 52a and the first posterior opening 38 a. As such, an anterior portion ofthe first channel 28 a defined between the first anterior opening 34 aand the first inflection point 52 a has a funnel shape. Specifically,the anterior portion of the first channel 28 a tapers to be narroweralong a length of the shank 18 from the first proximal opening 34 a tothe first inflection point 52 a, thereby defining a funnel shape. Aposterior portion of the first channel 28 a defined between the firstinflection point 52 a and the first posterior opening 38 a has acylindrical shape.

The first channel 28 a is threaded around its interior as illustrated.Despite the variation in the perimeter of the first channel 28 a, thefirst channel 28 a is threaded at a constant pitch from the firstposterior opening 34 a to the first posterior opening 38 a. An objectwith exterior threading, such as a screw, may therefore threadinglyengage the first channel 28 a along an entire length of the firstchannel 28 a. For more details regarding exemplary screws suitable forengagement with any of the nails of the present disclosure, referencemay be made to International Publication Number 2019/111041,corresponding to International Patent Application NumberPCT/IB2017/057688, filed on Dec. 6, 2017. Because the angle betweenfirst skew axis 47 and centered orthogonal axis 46 is relatively small,the threads of a screw securely engage the threaded portion at any partof first channel 28 a despite whether the screw may not be exactlyparallel to centered orthogonal axis 46 about which the threads of firstchannel 28 a are defined.

The second channel 28 b similarly defines a second distal edge 50 b thatextends perpendicular to the centerline X and a second proximal edge 54b that includes a second ramped portion 51 b defining a funnel shape incooperation with the second distal edge 50 b, a second orthogonalportion 53 b extending parallel to the second distal edge 50 b, and asecond inflection point 52 b between the second ramped portion 51 b andthe second orthogonal portion 53 b. The second channel 28 b defines aproximal orthogonal axis 56 and a distal orthogonal axis 58, bothperpendicular to the centerline X at their respective locations. Adistal portion of the second channel 28 b defines a half of a cylindercentered on the distal orthogonal axis, and a proximal portion of thesecond channel 28 b between the second inflection point 52 b and thesecond posterior opening 38 b defines a half of a cylinder centered onthe proximal orthogonal axis 56. The second channel 28 therefore has anobround cross section between the second inflection point 52 b and thesecond posterior opening 38 b. The second channel 28 b of theillustrated arrangement is not threaded, and may non-threadingly receivea transverse element such as a locking screw or nail for restrainingmovement of the nail 10 within the bone.

The second ramped portion 51 b extends both distally and posteriorlyfrom the second anterior opening 34 b to the second inflection point 52b. A second skew axis 57 is defined parallel to the ramped portion 51 b.In various arrangements, the second skew axis 57 extends at an angle ofbetween 3° and 7°, or 6.5°, relative to the proximal orthogonal axis 56.A proximal portion of the channel 28 b between the second anterioropening 34 b and the second inflection point 52 b defines a half of acylinder centered on the second skew axis 57. An anterior portion of thesecond channel between the second anterior opening 34 b and the secondinflection point 52 b therefore has a funnel shape that narrows relativeto the centerline X as it extends further in the posterior direction P,but has a constant width relative to a lateral direction that isperpendicular to the proximal orthogonal axis 56, distal orthogonal axis58, and second skew axis 57.

The foregoing description pertains to the illustrated arrangement, andnails 10 according to other arrangements differ in some respects to suitdifferent applications. For example, in some alternative arrangements,the orthogonal axes 46, 57, and 58, the distal edges 50 a, 50 b, and theorthogonal portions 53 a, 53 b of the proximal edges 54 a, 54 b extendat non-perpendicular angles relative to the centerline X at theirrespective locations along the centerline X.

The nail 10 is flexible such that typical forces on the shank 18 duringinsertion of the nail 10 into bone may cause the nail 10 to deflect inthe anterior direction A or posterior direction P within an expectedrange of deflection 62 as illustrated in FIG. 3 . In variousarrangements, the expected degree of deflection can be determinedempirically or by theoretical analysis of the nail 10, such as finiteelement analysis. A first theoretical cylinder 28 a extends through thefirst channel 28 a and a second theoretical cylinder 28 b extendsthrough the second channel 28 b throughout the expected range ofdeflection 62. The funnel shapes of the anterior portions of the firstchannel 28 a and second channel 28 b enable the distal portion 20 of theshank 18 to travel across the entire expected range of deflection 62while the first theoretical cylinder 60 a and second theoreticalcylinder 60 b remain stationary relative to the head 14 without eitherof the cylinders 60 a, 60 b crossing the boundary of either of theproximal edges 154 a, 154 b or distal edges 150 a, 150 b of the channels28 a, 28 b. As such, it is possible to install the nail 10 in a bone,then insert a cylindrical drill bit having a similar diameter to thetheoretical cylinders 60 a, 60 b in both channels 28 a, 28 b, followedby cylindrical locking elements such as bone screws of slightly largerdiameter than the theoretical cylinders 60 a, 60 b at predeterminedlocations relative to the head 14 without measuring actual deflection ofthe nail 10 in situ. Because the funnel shapes of the channels 28 a, 28b accommodate the theoretical cylinders 60 a, 60 b throughout theexpected range of deflection 62, the drill or drills will not damage thechannels 28 a, 28 b, or any threading therein, and cylindrical lockingelements inserted through the bone at the same position relative to thehead 14 as the cylinders 60 a, 60 b can be expected to extend cleanlythrough the channels 28 a, 28 b and to engage a portion of the threadedchannel to facilitate locking. Further, because of the elongatedthreading of the first channel 28 a, a blindly inserted bone screw canbe expected to threadingly engage the first channel 28 a regardless ofthe actual degree of deflection. Though the first channel 28 a isillustrated as fully threaded, in some alternative arrangements thefirst channel 28 a is only partially threaded. For example, in somearrangements, only the distal or proximal half of the first channel 28 ais threaded.

In some arrangements, the nail 10 may be constructed such that theexpected range of deflection 62 extends further in the posteriordirection than in the anterior direction relative to the head 14, asshown in FIG. 3 . Flexibility of the nail 10 may vary as appropriate fora given procedure. For example, the flexibility of the nail 10 maydepend on the size, shape, and density of the bone for which the nail 10is intended and the anticipated force to be applied to the nail 10during the procedure. In some arrangements, a ratio of the range ofdeflection 62 to a total length of the nail 10 is at least 1:30. Infurther arrangements, the ratio of the range of deflection to the totallength of the nail is 1:24. From left to right, FIG. 3 shows the distalportion 20 in an extreme anterior position, a middle position, and anextreme posterior position. The middle position is closer to the extremeanterior position than the extreme posterior position. In somearrangements, the middle position is three times farther from theextreme posterior position than the extreme anterior position. Theinclination toward posterior deflection can be designed into the nail 10by, for example, designing the nail to have a neutral position, meaninga position the nail 10 assumes in the absence of external forces,wherein the centerline X curves toward the posterior direction away fromthe head 14.

A portion of a nail 110 according to an alternative arrangement isillustrated in FIG. 4 . The shank 118 is cannulated and contains a bore164 extending along the centerline X. A channel 128 extending throughthe shank 118 is therefore provided by a chamfered anterior opening 134and a posterior opening 138 on opposite sides of the bore 164. Theanterior opening 134 is defined between an anterior distal edge 150 aand an anterior proximal edge 154 a, and the posterior opening 138 isdefined between a posterior distal edge 150 b and a posterior proximaledge 154 b. The posterior opening 138 has a circular cross-sectionalshape, and a cross-sectional shape of the anterior opening 134 has athickness defined perpendicular to the centerline X that is equal to adiameter of the posterior opening 138. The anterior opening 134 has anobround cross-sectional shape such that a distance between the anteriorproximal edge 150 a and the anterior distal edge 154 a is greater thanthe diameter of the posterior opening 138. Similar to the nail 10 asillustrated in FIG. 3 , the nail 110 is designed such that a theoreticalcylinder 160 at a given position relative to a head (not pictured) ofthe nail 110 may extend through the channel 128 at any degree ofdeflection of the shank 118 within a range of deflection expected toresult from insertion of the nail 110 into a bone. Specifically,respective locations and angles of the edges 150 a, 150 b, 154 a, 154 bof the channel 128 permit the shank 110 to deflect throughout theexpected range of deflection while the theoretical cylinder 160 remainsstationary without any of the edges 150 a, 150 b, 154 a, 154 bcontacting the theoretical cylinder.

In other arrangements, the distal portion 20 includes differing numbersand arrangements of anterior to posterior channels. For example, thedistal portion 20 may include only one, or three or more, anterior toposterior channels, and the relative widths along the centerline X ofthe anterior to posterior channels may have any pattern along thecenterline X. For example, the channel with the greatest width along thecenterline X may be a middle or proximal most channel of the channelsincluded in the distal portion.

Nails 10, 110 according to any of the foregoing examples may be designedaccording to empirically derived or mathematically determined values.Specifically, one or more sets of general dimensions of a nail 10, 110,such as length and diameter, may be predetermined. Ranges of curvatureof the nail 10, 110 to be expected during an implanting procedure may beestimated by experimentation with simulated implanting procedures,mathematically, such as by finite element analysis, or by a combinationof experimental and mathematical processes, for each predetermined setof general dimensions. Angles and dimensions of channels through thenails 10, 110 of the various predetermined general dimensions may thenbe determined in view of the expected range of curvature and thediameters of any associated drills or bone screws. Specifically, eachchannel for a given set of predetermined general dimensions may belocated, angled, and dimensioned such that an associated drill may bedriven through the bone and channel at a predetermined location andangle relative to a head of the nail 10, 110 without damaging thechannel or any threading internal to the channel, and a bone screw maybe engaged through the channel at a predetermined location and anglerelative to a head of the nail 10, 110, after the nail 10, 110 has beenimplanted, for any position of the nail 10, 110 within the expectedrange of curvature. A nail 10, 110 designed according to the foregoingprocess may therefore be implanted into a bone and secured in place withtransverse bone screws without an intervening step of determining theactual degree of curvature of the nail 10, 110.

Illustrated in FIG. 5 is a targeting device 200 for preparing a femur210 in a retrograde guided targeting drilling procedure. This proceduresecures a nail 10, 110 after the nail 10, 110 has been inserted into thefemoral canal. The targeting device 200 includes a bracket 214connectable to the head of the nail 10, 110. The bracket 214 holds anarm 218 of the targeting device 200 at a location that can be adjustedfor each specific use depending on the patient anatomy. The arm 218 endsin a block 222 containing two guide holes 226 a, 226 b for guiding adrill and a fastener through the femur 210 and nail 10. Guide holes 226a, 226 b are specifically dimensioned and positioned to coincide withchannels 28 a, 28 b of nail 10 to allow locking of nail 10 within thefemur. That is, block 222 is positioned with respect to the femur 210such that both guide holes 226 a, 226 b will direct the drill andsubsequent screws or pins through the channels 28 a, 28 b, respectively,without the drill contacting the edges of the channel.

Guide hole 226 a is cylindrical and is angled at 3° from an axis that isperpendicular to a centerline of block 222, which is designed to beparallel to the centerline X of nail 10 when nail 10 is at rest orundeflected in the position (B) shown in FIG. 6 . The 3° anglecorresponds to the geometry of channel 28 a and allows predrilling witha drill, of 4.2 mm for example, without any metal contact in deflectedand undeflected nails when used with channel 28 a. Also shown in FIG. 6are a position (A) depicting the nail in anterior deflection, and aposition (C) depicting the nail in posterior deflection. The 3° angle ofguide hole 226 a coincides with the geometry and orientation of channel28 a so that a drill bit or a screw passed through guide hole 226 awould pass through a central portion of channel 28 a with nail 10 atrest, i.e. along an axis coincident with or between first skew axis 47and centered orthogonal axis 46 depending on the flexion state of nail10. Guide hole 226 a is tilted at 3° such that an axis through thecenter of guide hole 226 a and centered orthogonal axis 46 of firstchannel 28 a intersect at the center of the uppermost part of thecylindrical zone of channel 28 a, i.e. aligned with first inflectionpoint 52 a. Guide hole 226 b is similarly angled at 3° with respect toproximal orthogonal axis 56 of second channel 28 b to provide the samecooperation between guide hole 226 b and second channel 28 b as isdescribed above between guide hole 226 a and first channel 28 a. Guidehole 226 b is oblong for static/dynamic locking in second channel 28 b.

Since guide hole 226 a is tilted at 3°, first channel 28 a is configuredso that a drill passed through first channel 28 a will not contacteither first ramped portion 51 a or first distal edge 50 a despite anydeflection in nail 10. This is shown in FIG. 6 , where position (A)coincides with anterior deflection of nail 10, yet nail 10 is alignedsuch that first distal edge 50 a is close to axial alignment with thedrill bit. In position (C) showing posterior deflection of nail 10, nail10 is aligned such that first ramped portion 51 a is close to axialalignment with drill bit. The angle of 6.5° of first ramped portion 51 aand the angle of 0° of first distal edge 50 a have been empiricallydetermined so that the 3° angle of 226 a can facilitate drilling withoutmetal contact or any alteration of the interior threads of first channel28 a. The 0° angle of first distal edge 50 represents the locking holeposition without the funnel function, such that it represents theorientation of all round holes perpendicular to the nail axis. Thedesign was chosen so that the least material was removed compared to theround hole of previous designs. This testing has focused on the range ofdeflection angles of nail 10 given various contours and shapes of femursto focus the angle range to a zone that encompasses substantially allpotential values of deflection. This results in substantially allprocedures resulting in no metal contact between the drill and firstchannel 28 a. Accordingly, during targeting and drilling through thetargeting device, the nail should not be damaged, either in undeflectedor in deflected position.

After guide holes 226 a, 226 b are used to guide the drill through thefemur 210, fasteners or screws 228 may be inserted through the drilledholes and channels 28 a, 28 b, 128 to secure the nail 10, 110 to thefemur 210. Since channels 28 a, 28 b, 128 are obround, the screws 228are able to engage with the internal threads of channels 28 a, 28 b, 128despite whatever deflection may exist in nail 10. For example, channel28 a has a lateral width throughout that is the same as the diameter ofchannel 28 a in the cylindrical zone below the first inflection point 52a. This is despite the fact that the proximal-distal dimension ofchannel 28 a increases in a direction upward and away from firstinflection point 52 a. in that way, when a screw 228 is inserted at anextreme deflection state of nail 10, it will engage the screw threads atfirst ramped portion 51 a or first distal edge 50 a, in addition toengaging the internal threads at the lateral sides of channel 28 a andthe internal threads of the cylindrical zone below the first inflectionpoint 52 a. At any angle between these extremes, the screw 228 willengage the screw threads at least at the lateral sides of channel 28 aand the internal threads of the cylindrical zone below the firstinflection point 52 a. Although the threaded connection may not be aperfect match, the range of angles permits threaded engagement of thescrew within channel 28 a despite the angle at which the screw 228 isinserted. Once the screw enters the cylindrical zone between firstorthogonal portion 53 a and first distal edge 50 a, which is below firstinflection point 52 a, the cylindrical nature of this portion of channel28 a reorients the screw so that it is finally positioned perpendicularto the axis of the nail like in normal round holes. Of course in someinstances this reorientation of the screw may not result in a completelyperpendicular orientation. In those instances, the geometry andcontouring of channel 28 a is utilized to facilitate secure locking of ascrew 228 regardless of what deflection may be present in an implantednail 10, which eliminates the need for a user to be concerned withfinely tuned and precise angling of screw insertion during a procedure.Of course, channel 28 a is described herein as an example in thismethod, and channels 28 b and 128 are designed in the same manner whileaccounting for their oblong shape.

Although the concepts herein have been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present disclosure as defined by the appended claims.

The invention claimed is:
 1. An intramedullary nail comprising: a shankwith a centerline defined along a length thereof; and said shank havinga channel with a channel axis perpendicular to the centerline, thechannel having an obround shape in a first cross-sectional planeperpendicular to the channel axis at the centerline and a taperedprofile in a second cross-sectional plane containing the channel axis,such that a portion of a proximal edge of the channel within the secondcross-sectional plane forms a first angle relative to the channel axisand a distal edge of the channel within the second cross-sectional planeforms a second angle relative to the channel axis that is different fromthe first angle, wherein the channel is internally threaded.
 2. Theintramedullary nail of claim 1, wherein opposed proximal and distal endsof the channel are each defined by a round surface extending alongrespective non-parallel axes, and opposed sides of the channel areplanar and extend between the two round surfaces to define the obroundshape.
 3. The intramedullary nail of claim 2, wherein an extensionportion of the channel defines a circular opening at a surface of theshank.
 4. The intramedullary nail of claim 2, wherein the twonon-parallel axes each intersect the centerline.
 5. The intramedullarynail of claim 2, wherein the first angle is non-zero and the secondangle is zero.
 6. The intramedullary nail of claim 2, wherein the nailincludes an obround opening in the shank that feeds into the channel,and at least part of a perimeter of the obround opening is chamfered. 7.The intramedullary nail of claim 2, wherein an angle between the twonon-parallel axes is between 3° and 7°.
 8. The intramedullary nail ofclaim 7, wherein the angle between the two non-parallel axes is 6.5°. 9.The intramedullary nail of claim 2, wherein: a portion of the roundsurface of the proximal end of the channel defines a half of a cylindercentered on the proximal axis, and a portion of the round surface of thedistal end of the channel defines a half of a cylinder centered on thedistal axis.
 10. The intramedullary nail of claim 1, wherein: the shankis capable of elastic deformation across a range of deflection on thesecond cross-sectional plane, a ratio of a distance travelled by adistal tip of the shank between opposite ends of the range of deflectionto a total length of the nail being at least 1:30; and a rectangulararea exists on the second cross-sectional plane that does not intersecta proximal or distal edge of the channel at any position of the shankwithin the range of deflection.
 11. The intramedullary nail of claim 10,wherein the ratio of the range of deflection of the distal tip of theshank to the total length of the nail is 1:24.
 12. The intramedullarynail of claim 1, wherein the shank defines a bore extending along thecenterline and dividing the channel into two aligned passages.
 13. Amethod for treating injury to a bone, comprising: inserting anintramedullary nail into an intramedullary canal of the bone generallyalong the anatomical axis of the bone, wherein the nail includes: ashank with a centerline defined along a length thereof; and said shankhaving a channel with a channel axis perpendicular to the centerline,the channel having an obround shape in a first cross-sectional planeperpendicular to the channel axis at the centerline and a taperedprofile on a second cross-sectional plane containing the channel axis atthe centerline, wherein the channel is internally threaded; andinserting a screw through a predetermined location of the bone such thatthe screw threadingly engages at least a portion of the channel.
 14. Themethod of claim 13, wherein the nail includes an obround opening in theshank that feeds into the channel, and the nail is implanted in the bonewith the obround opening oriented in an anterior direction relative tothe bone.
 15. The method of claim 14, wherein the nail is implanted inthe bone such that the tapered profile narrows toward a posteriordirection relative to the bone.
 16. The method of claim 15, furthercomprising drilling through the bone and the channel at a predeterminedlocation of the bone from the anterior direction toward the posteriordirection.
 17. The method of claim 13, wherein the screw engages atleast a portion of the channel to accommodate flexion of theintramedullary nail that occurs during implantation.
 18. A method ofdesigning an intramedullary nail, comprising: estimating an anticipatedrange of flexion of a shank of an intramedullary nail on a flexion planecorresponding to flexion of the nail during a procedure for implantingthe nail in a bone; defining a fixed position for a cylindrical fixationelement relative to a head of the nail, the head located at a proximalend of the nail, the fixed position being such that the cylindricalfixation element would extend transverse to and intersect the shank atany position of the shank within the anticipated range of flexion; andselecting respective locations and angles for a proximal extremity of achannel disposed through a distal half of the shank and a distalextremity of the channel such that the cylindrical fixation elementlocated at the fixed position would extend through the channel withoutcrossing the proximal extremity or the distal extremity of the channelat any degree of flexion of the shank within the anticipated range offlexion.
 19. The method of claim 18, further comprising: defining anadditional fixed position for an additional cylindrical fixationelement; and selecting respective locations and angles for proximal anddistal extremities of an additional channel disposed through the distalhalf of the shank such that the additional cylindrical fixation elementlocated at the additional fixed position would extend through theadditional channel without crossing the proximal or distal extremity ofthe additional channel at any degree of flexion of the shank within theanticipated range of flexion.
 20. A method for treating injury to a boneusing an intramedullary nail designed according to the method of claim18, the method comprising: inserting the nail into the bone generallyalong the anatomical axis of the bone while allowing flexion of the nailwithin the bone; and after the nail is inserted into the bone, insertinga screw through the bone and channel at a location and angle relative tothe head of the nail corresponding to the fixed position of thecylindrical fixation element.